In the course of investigating the efficiency of feed use, the mechanism by which cattle, sheep and other ruminants digest and degrade the components of their feed to form metabolities has been intensively studied. The mechanism of carbohydrate metabolism is well known. Microorganisms in the rumen of the animal ferment ingested carbohydrates to produce monosaccharides which in turn are degraded to pyruvate derivatives.
The pyruvates in turn are metabolized to either an acetate or a propionate which may exist as acids, salts, or other radicals. Butyrates are usually formed from two acetate radicals.
The animal can utlize butyrate, propionate, and acetate with differing degrees of efficiency. Utilization of these compounds, which are collectively known as volatile fatty acids (VFA), occurs after absorption from the gut of the animal. Butyrate is utilized most efficiently, and acetate the least efficiently. However, the overall efficiency of utilizing butyrate is lower than that of propionate, because extra energy is consumed during the formation of butyrate from two acetate molecules.
Generally, it is established that the higher the efficiency of carbohydrate utilization, the higher the feed efficiency. In other words, the feed efficiency can be effectively monitored by observing the production and concentration of propionate in the rumen. If the animal is generating more propionate in its rumen, it will be found to be utilizing its feed more efficiently.
This invention relates to the combination of thiopeptin or other related sulfur-containing cyclic polypeptides with a pyromellitic diimide. When the two compounds are combined and administered to ruminants, a synergistically favorable shift in "ruminal parameters" is observed which represents an improved feed efficiency. "Ruminal parameters" generally refers to the volatile fatty acid (VFA) content of the animal rumen, the methane gas content, and the total gas content. As discussed above, a shift of VFA to higher propionate content and lower acetate-methane contents indicate a higher feed efficiency. For the novel combination of the present invention, the favorable shift is found to be surprisingly greater than the mere sum of the corresponding individual shifts, i.e., the shift caused by the combination is greater than the sum of the shifts when the individual compound is fed alone to the animals.